1. Field of the Invention
The present invention relates to a radial arm saw that comprises a column standing erect on a base, a guide arm supported on the column in such a manner that it is vertically movable by an adjuster, and a saw member that is equipped with a motor and a circular saw blade and which is supported on the guide arm in such a manner that it is movable back and forth and is rotatable in two axial directions.
2. Background of the Invention
The conventional mechanism for sliding the saw member in the radial arm saw has the following construction: two opposing semicircular grooves are formed longitudinally in the inner surface of the side walls of the guide arm. Bearings that match these semicircular grooves are rotatably supported on the side walls of a bearing holder that supports the saw member and which is fitted in the guide arm. These bearings are fitted in the semicircular grooves so that the saw member can be guided along the guide arm in its longitudinal direction.
It is difficult to assemble the blade sliding mechanism in such a manner that no rattling will occur between individual components and that the bearing holder is accurately positioned at a predetermined angle horizontally or in other attitudes. Therefore, after assembling the mechanism, selected components are moved by the necessary amount to absorb any rattling that occurs and the bearing holder is adjusted to be positioned at a predetermined angle. In the prior art, the rattling in the guide section is absorbed by moving the bearings in their radial direction and the inclination of the bearing holder at a small angle is adjusted by moving the bearings in their axial direction. However, biaxial movement of the bearings is time-comsuming and adjusting them properly is a tedious and difficult job that can only be achieved by skilled personnel. In addition, the bearings must be specialty products that have semicircular outer races. Therefore, the conventional blade sliding mechanism for use in a radial arm saw has problems not only in their manufacture but also with regard to economy.
Various constructions are known to be usable as the mechanism for locking the sliding of the saw member in a radial arm saw but they are disadvantageous in one way or another in that they are complicated or require tedious procedures in locking or unlocking the blade.
In the radial arm saw, the guide arm is supported on the base in such a manner that it is vertically slidable by an adjuster, and the saw member is mounted on the guide member in such a manner that it is movable back and forth and is rotatable through adjustment of a vertical shaft. In addition, the blade angle is adjustable with a support shaft perpendicular to the vertical shaft being used as a fulcrum.
The saw member is rotatably supported in such a manner that the blade angle can be altered with respect to a frame that is mounted on the guide in a longitudinally movable and adjustably rotatable manner. In the prior art, a motor case is rotatably supported on the frame with a pinon, the case being pressed with a suitable device such as a cam. This arrangement, however, is complicated and expensive while it fails to achieve speedy adjustment of the blade angle.
The adjuster in the conventional radial arm saw comprises a cylindrical column that is erected on the base and a guide holder that is provided with an elongated slot and which is slidably fitted over the column. Key grooves are formed in the mating surfaces of the guide holder and the column and a key is fitted into these grooves so as to secure the guide holder against rotation. A saw guide arm is supported on the guide holder and a feed screw equipped with a handle is rotatably supported on this guide arm while it is prevented from making any axial movement. The feed screw is threaded into a threaded hole made in the column and by operating the handle to turn the feed screw clockwise or counterclockwise, the guide holder is caused to ascend or descend along the column so as to effect vertical movement of the guide arm.
The guide holder is also equipped with a clamping handle which is operated to clamp the guide holder such that it is reduced in diameter and is securely fixed to the column.
In the prior art, the key grooves formed in the mating surfaces of the guide holder and the column are channel-shaped and a key having squire cross section is fitted in these grooves. Therefore, even if the guide holder provided with an elongated slot is reduced in diameter by clamping with the handle, the engagement between each key groove and the key is not completely free from rattling and the guide holder cannot be completely secured against rotation. Conventionally, a combination of a key retainer and a retaining screw is used to eliminate the rattling between the key grooves and the key but this is not desirable from the viewpoint of reducing the number of parts used. In addition, the key retainer or retaining screw may come off as a result or repeated loosening or tightening operations with the handle that are performed for the purpose of sliding the guide holder vertically or fixing it to the column. Therefore, the adjuster in the conventional radial arm saw has problems not only in manufacture and economy but also with respect to its use.
To ensure utmost safety, the radial arm saw establishes dual insulation of the switch mounting section and this calls for the need to cover the wiring port with an insulator. In the prior art, the switch mounting section consists of a switch case that is covered with a switch cover formed as a separate member and the wiring (i.e., power cables) is mounted in the switch case with a cable retainer or some other fastening device being used to hold the cables in position. This arrangement, however, requires at least three parts, viz., the switch case, the switch cover, and the cable retainer. In addition, different securing means are necessary to attach these parts and much time is spent in manufacturing and assembling the respective parts of the switch mounting section, which is undesirable from an economic viewpoint.
The radial arm saw is equipped with a safety cover for the circular saw blade and other means that provide safety for the operator during the operation of the saw. The motor is turned off when the saw member is moved vertically or the angle of cutting with the circular saw blade is adjusted. An ON-switch button and an OFF-switch button are provided on a selected component, typically on the guide plate, for turning the motor on and off. If these buttons are disposed to protrude from the guide plate such that they can be readily depressed, there is a high likelihood that the motor is turned on as a result of erroneous depression of the ON-switch button during the vertical movement of the blade member or the adjustment of the blade angle. In order to eliminate this potential hazard, it has been proposed that the ON-switch button is locked in an OFF state (i.e, disabled ON mode) but the locking mechanisms so far proposed are complicated in construction or liable to become unlocked accidentally if they are disposed to protrude from the guide plate.
Conventionally, the lead wire cover in the radial arm saw is either formed as an integral part of the guide arm or attached to the latter by a suitable means such as screws. However, the lead wire cover is fabricated without any regard to the switch or other associated parts, so that it cannot be integrated in the assembly in an economic manner and great difficulty if involved in holding power cables in position.
In the radial arm saw, a single column is erected at one end of the base and one end of the guide arm is cantilevered on the column and is slidably supported by an adjuster. The guide arm supports a bearing holder that is fitted to be guided by the arm, a frame that is rotatably supported in the bearing holder by a vertical shaft, and a saw member that is rotatably supported in the frame by a horizontal shaft. The base is required to support these heavy-duty members. There is another reason for the need to provide a rigid structure for the base. The work on the table must be correctly cut with the saw member that is pushed forward with the motor-driven circular saw revolving continuously.
In the prior art, the column retaining holder is mounted on the base that is formed of a solid member which itself has the necessary rigidity. However, this arrangement is inevitably complicated and not only the production cost but also the weight of the base is increased.
In the conventional radial arm saw, the table for holding the work is secured to a base, or table angle irons fixed thereto, with wood screws being inserted through mounting holes in the base or table angles and threaded into the table. However, this mounting method is not efficient and is quite time-consuming since the wood screws must be threaded each time the table is to be mounted or removed whenever the table is dismounted. In addition, low precision in the threading of wood screws may cause incorrect mounting of the table.
In order to ensure a maximum degree of safety, the saw member in the radial arm saw is equipped with not only a safety guard which covers the upper half of the circular saw but also a single lower guard that covers the lower half of the circular saw blade when it is not revolving but which is rotated upward by the work as it is progressively cut with the saw. In the prior art, the lower guard is simply mounted in such a manner that one end thereof is pivotally supported in an appropriate area of the saw member so as to permit the guard to rotate either upwardly or downwardly. But this arrangement often causes irregular rotation of the lower guard or insecure covering of the circular saw as a result of its displacement in a longitudinal direction which is perpendicular to the direction of its rotation or tilting of the lower guard in some other direction.